Service Handbook - AO Smith Water Heaters

Pressure Switch Tests
Complete pressure switch testing involves three procedures:
• Continuity Test During Standby below.
• Continuity Test During Operation on page 32.
• Pressure Test During Operation on page 32.
Continuity Test During Standby
This test is performed while the Combustion Blower is not running with the water heater turned off. This is a
"normal state" continuity test of the contacts inside each pressure switch. Disconnect the two wires to each
pressure switch for this test.
1. If the water heater is in a heating cycle lower the Operating Set Point to end the cycle, see Temperatures
on page 49.
2. Turn off power to the water heater at the water heater's on/off switch.
3. Disconnect both wires at each pressure switch.
4. Using an ohm meter set for continuity testing, check for continuity between the two wiring terminals at
each pressure switch, see Figure 33 below.
Results/Actions
Passed Results: If the Blower Prover switch contacts are open during this test (infinite ohms/open circuit)
the Blower Prover switch has passed the test. If the Blocked Intake Air and Blocked Exhaust switch contacts
are closed during this test, (zero ohms/direct short), these switches have passed the test.
Failed Results: If the Blower Prover switch contacts are closed (zero ohms/direct short) during this test, the
Blower Prover switch must be replaced. If the Blocked Intake Air and/or Blocked Exhaust switch contacts are
open during this test, the switch(s) must be replaced.
Proceed to the Continuity Test During Operation on page 32.
Figure 33
Servicing should only be performed by a Qualified Service Agent
31